Today's spark plugs have a center electrode and at least one ground electrode. During normal operation of the spark plug, an ignition spark that ignites a combustible gas mixture forms between the electrodes. Typically, the center electrode or ground electrode are made up of an electrode base body and a wear surface situated thereon that contains noble metal. Generally, the wear surface has a higher resistance to oxidation and corrosion, and thus has a lower degree of wear, than does the material of the electrode base body. The wear surface is connected with a material bond to the respective electrode base body by welding. There are various welding techniques, such as resistance welding, laser welding, or electron beam welding, that are used in the production of spark plugs.
Due to the different material properties of the wear part and the electrode base body, in particular the significantly higher melting temperature of the wear part material, the production of a reliable and long-lasting material bond of the two components poses a challenge.
In addition, there is the fact that on the one hand the desired resistance to wear of the wear parts, containing noble metal, is reduced in fused regions of the wear part. In order nonetheless to achieve the desired durability for the electrode and thus also for the spark plug, a certain minimum volume of the unmodified material containing noble metal is required. On the other hand, the noble metal required for a wear part is relatively expensive, so that in principle it is desirable to keep the volume containing noble metal small.
For electrodes having wear parts that have a smaller radius compared to their height, there are bonding methods that provide an acceptable compromise between long life of the welded bond, of the wear part, and of the spark plug, as well as production costs.